Prevent races between dropping File LockGuard and waking its tasks #1056
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By changing the inner `LockGuard` value to an `Option` and setting it to `None` in `drop()` so we can drop the `Arc` _before_ waking its tasks.
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By changing the inner
LockGuardvalue to anOptionand setting it toNoneindrop()so we can drop theArcbefore waking its tasks.Closes #1001
I have not added a regression test, because the only practical test I can think of is the busy loop, but I don't think we want a test like that.
I can easily reproduce the panic without the fix (the test crashes within 0.1-7 seconds on my machine), but with the fix I get no crash (I waited for 8 minutes).
To be honest I am not 110% sure that the fix is 100% sound, but intuitively this feels like a good fix. Maybe it is obviously correct (or obviously wrong) to people who are more familiar with this code base. I'm confident enough in the fix to consider it ready for CR at least.